{{short description|Organic compound with formula C2(CN)4}} {{chembox |Watchedfields = changed |verifiedrevid = 470603691 |Name = Tetracyanoethylene |ImageFileL1 =Tetracyanoethylene.png |ImageFileR1 = TCNE3D.png |ImageSizeR1 = 150px |ImageNameR1 = tetracyanoethylene |ImageFile2 = TCNEpowder.jpg |PIN = Ethenetetracarbonitrile |OtherNames = TCNE |Section1={{Chembox Identifiers |ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |ChemSpiderID = 12114 |PubChem = 12635 |InChI = 1/C6N4/c7-1-5(2-8)6(3-9)4-10 |InChIKey = NLDYACGHTUPAQU-UHFFFAOYAN |StdInChI_Ref = {{stdinchicite|correct|chemspider}} |StdInChI = 1S/C6N4/c7-1-5(2-8)6(3-9)4-10 |StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} |StdInChIKey = NLDYACGHTUPAQU-UHFFFAOYSA-N |CASNo_Ref = {{cascite|correct|CAS}} |CASNo = 670-54-2 |UNII_Ref = {{fdacite|correct|FDA}} |UNII = C592309ECU |SMILES = N#CC(C#N)=C(C#N)C#N }} |Section2={{Chembox Properties |Formula = {{chem2|C2(CN)4}} |C=6|N=4 |Density = 1.35 g/cm<sup>3</sup> |MeltingPtC = 199 |BoilingPtC = 130 to 140 |BoilingPt_notes = 0.1 mmHg (sublimes)<ref name=Carboni>{{OrgSynth | journal=Org. Synth.|author = Carboni, R. A. | title = Tetracyanoethylene | volume = 39 | pages = 64 | year = 1959 | doi = 10.15227/orgsyn.039.0064}}</ref> }} }}
'''Tetracyanoethylene''' ('''TCNE''') is organic compound with the formula {{chem2|C2(CN)4}}. It is a colorless solid, although samples are often off-white. It is an important member of the cyanocarbons.
==Synthesis and reactions== TCNE is prepared by brominating malononitrile in the presence of potassium bromide to give the KBr-complex, and dehalogenating with copper.<ref name=Carboni/>
Oxidation of TCNE with hydrogen peroxide gives the corresponding epoxide, which has unusual properties.<ref name=linn73>{{OrgSynth | author = Linn, W. J. | title = Tetracyanoethylene Oxide | volume = 49 | pages = 103 | year =1969 | doi = 10.15227/orgsyn.049.0103}}</ref>
In the presence of base, TCNE reacts with malononitrile to give salts of pentacyanopropenide:<ref>{{cite journal |first1= W. J.|last1=Middleton|first2=D. W.|last2=Wiley|doi=10.15227/orgsyn.041.0099|title=Tetramethylammonium 1,1,2,3,3-Pentacyanopropenide |journal=Org. Synth.|year=1961|volume=41|page=99}}</ref> :{{chem2|C2(CN)4 + CH2(CN)2 → [(NC)2C\dC(CN)\sC(CN)2]- + CN- + 2 H+}}
==Redox chemistry== TCNE is an electron acceptor. Cyano groups have low energy π* orbitals, and the presence of four such groups, with their π systems (conjugated) to the central {{chem2|C\dC}} double bond, gives rise to an electrophilic alkene. TCNE is reduced at −0.27 V vs ferrocene/ferrocenium:<ref name=Geiger>{{cite journal|first1=N. G.|last1= Connelly|first2= W. E.|last2= Geiger| title=Chemical Redox Agents for Organometallic Chemistry|journal=Chemical Reviews|year= 1996| volume= 96|issue=2| pages= 877–910| doi=10.1021/cr940053x| pmid=11848774}}</ref> :{{chem2|C2(CN)4 + e- → [C2(CN)4]-}} Because of its ability to accept an electron, TCNE has been used to prepare numerous charge-transfer salts<ref name=chittipeddi87>{{cite journal | last1=Chittipeddi | first1=Sailesh | last2=Cromack | first2=K. R. | last3=Miller | first3=Joel S. | last4=Epstein | first4=A. J. | title=Ferromagnetism in Molecular Decamethylferrocenium Tetracyanoethenide (DMeFc TCNE) | journal=Physical Review Letters | volume=58 | issue=25 | date=1987-06-22 | issn=0031-9007 | doi=10.1103/physrevlett.58.2695 | pages=2695–2698| pmid=10034821 | bibcode=1987PhRvL..58.2695C}}</ref> and magnetic molecular materials.
The central C=C distance in TCNE is 135 pm.<ref>{{cite journal |doi=10.1021/ja00804a010 |title=Valence electron distribution in cubic tetracyanoethylene by the combined use of x-ray and neutron diffraction |date=1973 |last1=Becker |first1=P. |last2=Coppens |first2=P. |last3=Ross |first3=F. K. |journal=Journal of the American Chemical Society |volume=95 |issue=23 |pages=7604–7609 }}</ref> Upon reduction, this bond elongates to 141–145 pm, depending on the counterion.<ref>{{cite journal |doi=10.1021/ic00050a032 |title=Structures of charge-perturbed or sterically overcrowded molecules. 16. The cesium tetracyanoethylenide radical salt |date=1992 |last1=Bock |first1=H. |last2=Ruppert |first2=K. |journal=Inorganic Chemistry |volume=31 |issue=24 |pages=5094–5099 }}</ref>
==Safety== TCNE hydrolyzes in moist air to give hydrogen cyanide and should be handled accordingly.<ref name = Carboni/>
==References== {{reflist}}
Category:Alkene derivatives Category:Nitriles Category:Superconductors